Self-watering pots

In short

Self-watering pots hold a reservoir of water below the mix and let the mix draw water up by capillary action or a wick. They conserve water and let you leave plants for a few days, but soluble salts cannot be flushed down and out, so they build up over time.

How it looks

A container with a separate water reservoir at the base, a perforated platform or wick connecting the mix to the water, usually a fill tube or spout and a water-level indicator, and an overflow hole on the side instead of drainage holes in the bottom.

Signs

Mix that stays evenly moist from below. White crusts on the mix surface or pot rim show salt build-up.

What favours it

They need a suitable light potting mix: Mississippi State University warns that native garden soil or bagged media meant for amending in-ground beds have the wrong physical properties for these containers. In hot weather the reservoir may need filling every day to keep the upward flow of water going.

Prevention

• Use a light potting mix suited to sub-irrigation, never garden soil.
• Check the reservoir often; Mississippi State University advises filling it daily in hot weather so capillary flow does not stop.
• Do not add soluble fertiliser to the reservoir, which Mississippi State University warns can raise salt levels enough to burn roots; it suggests a narrow band of granular fertiliser on top of the mix instead.

Treatment

Start with the first step and move down only if the problem persists.

1. If salt crust builds up, replace the top layer of mix or repot into fresh mix.

Pros and cons

Look-alikes

Salt and fertiliser burn

Brown leaf tips on a plant in a self-watering pot often come from salts that have nowhere to drain.

Typical uses

Widely used for container vegetables such as tomatoes; also used for other container plants.

Related

• Pot materials
• Watering technique
• Drainage in containers
• Salt and fertilizer burn
• Fungus gnats
• Overwatering

Sources

1. Sub-irrigated planter (Self-watering container) — Wikipedia
2. Self-Watering Containers — University of Maryland Extension
3. Subirrigated Containers for the Mississippi Gardener — Mississippi State University Extension

Written in our own words from these sources. Check a product label before using any treatment.